Etymology
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herpes (n.)

late 14c., "any inflammatory, spreading skin condition" (used of shingles, gangrene, etc.), from Latin herpes "a spreading skin eruption," from Greek herpes, the name for the disease shingles, literally "creeping," from herpein "to creep, move slowly" (cognate with Latin serpere "to creep;" see serpent). The condition was not distinguished into specific diseases until early 19c.

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rash (n.)

"eruption of small red spots on skin," 1709, perhaps from French rache "a sore" (Old French rasche "rash, scurf"), from Vulgar Latin *rasicare "to scrape" (also source of Old Provençal rascar, Spanish rascar "to scrape, scratch," Italian raschina "itch"), a variant of classical Latin rasitare, from Latin rasus "scraped," past participle of radere "to scrape" (see raze (v.)). The connecting notion would be of itching. The figurative sense of "any sudden outbreak or proliferation" is recorded by 1820.

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*red- 

*rēd-, Proto-Indo-European root meaning "to scrape, scratch, gnaw."

It forms (possibly) all or part of: abrade; abrasion; corrode; corrosion; erase; erode; erosion; radula; rascal; rase; rash (n.) "eruption of small red spots on skin;" raster; rat; raze; razor; rodent; rostrum; tabula rasa.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit radati "scrapes, gnaws," radanah "tooth;" Latin rodere "to gnaw, eat away," radere "to scrape;" Welsh rhathu "scrape, polish."

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hangnail (n.)

also hang-nail, "sore strip of partially detached flesh at the side of a nail of the finger or toe," probably a 17c. or earlier folk etymology and sense alteration (as if from hang (v.) + (finger) nail) of Middle English agnail, angnail "a corn on the foot," from Old English agnail, angnail. The literal sense probably is "painful spike" (in the flesh). The first element would be Proto-Germanic *ang- "compressed, hard, painful" (from PIE root *angh- "tight, painfully constricted, painful"). The second element is Old English nægl "spike" (see nail (n.)).

Compare Old English angnes "anxiety, trouble, pain, fear;" angset "eruption, pustule." OED also compares Latin clavus, which "was both a nail (of iron, etc.) and a corn on the foot." Similar compounding in Old High German ungnagel, Frisian ongneil.

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dormant (adj.)

late 14c., "fixed in place," from Old French dormant (12c.), present participle of dormir "to sleep," from Latin dormire "to sleep," from PIE root *drem- "to sleep" (source also of Old Church Slavonic dremati "to sleep, doze," Greek edrathon "I slept," Sanskrit drati "sleeps").

Meaning "in a resting situation, lying down with the head on the forepaws" (in heraldry, of beasts) is from c. 1500. Meaning "sleeping, asleep" is from 1620s. General sense of "in a state of rest or inactivity" is from c. 1600. Of volcanoes from 1760.

The Neapolitans are never so much afraid of this fiery Mountain as when its Flames lie, as 'twere, dormant ; for then it is that they live in constant Fear of a fresh huge Eruption, or, much worse, an Earthquake. [from the entry for "Vesuvius" in Brice's "Grand Gazetter Or Topographic Dictionary," 1760]
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typhus (n.)

acute infectious fever, usually accompanied by prostration, delirium, and small reddish spots, 1785, from medical Latin, from Greek typhos "stupor caused by fever," literally "smoke," from typhein "to smoke," related to typhos "blind," typhon "whirlwind," from PIE *dheubh-, perhaps an extended form of PIE root *dheu- (1) "dust, vapor, smoke." 

The Greek term [typhos] (smoke, mist, fog) was employed by Hippocrates to define a confused state of the intellect, with a tendency to stupor (stupor attonitus); and in this sense it is aptly applied to typhus fever with its slow cerebration and drowsy stupor. Boissier de Sauvages first (in 1760) called this fever "typhus," and the name was adopted by Cullen of Edinburgh in 1769. Previous to the time of de Sauvages typhus was known as "Pestilential" or "Putrid Fever," or by some name suggested by the eruption, or expressive of the locality in which it appeared, as "Camp," "Jail," "Hospital," or "Ship Fever" (Murchison). [Thomas Clifford, ed., "A System of Medicine," New York, 1897]

Related: typhous (adj.).

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